Microsoft has also benefited from growth in its cloud business. The stock is up 11% this year and is not far from a record high.

If the four biggest tech companies all hit the trillion dollar milestone relatively soon, they eventually may wind up being joined by a few other tech giants -- and a much older school conglomerate as well.

Facebook, Chinese e-commerce giant Alibaba and Chinese gaming and social networking kingpin Tencent are all worth about half a trillion dollars. So is Warren Buffett's Berkshire Hathaway.

There's also the possibility that none of these tech companies will be the first to top the magical trillion dollar level.

That's because oil giant Saudi Aramco is hoping to go public sometime this year -- and it is expected to be valued somewhere between $1.5 trillion and $2 trillion.